Heart failure is a major global health problem resulting in many thousands of deaths each year. Until recently, the only curative treatment for advanced heart failure has been a heart transplant or an implantation of a Total Artificial Heart (TAH). Unfortunately, the number of donor heart's only meets a tiny fraction of the demand and TAHs have yet to gain widespread acceptance due to the inherent technical difficulties.
Ventricular Assist Devices (VAD) have been gaining increased acceptance over the last decade, primarily as bridge-to-transplant devices. VADs are designed to be long-term implants and work alongside a diseased heart to boost its output and keep the patient alive and/or give a better quality of life whilst awaiting transplant.
The use of VADs has shown that, in most cases, once the device has been implanted, the heart failure does not progress any further and the patient regains a good quality of life. In cases where a heart transplant has not been available, patients have lived for several years using VAD therapy without major complications. Therefore, a VAD can be considered a viable alternative to heart transplantation and offers hope to the many thousands of heart failure patients for whom a donor heart will not be available.
At present, the main reasons preventing VADs from being fitted on a routine basis are the invasive surgical procedure required to fit the devices, and the high cost of the devices themselves. With regard to the surgery, typically a sternotomy and a full heart-lung bypass are required to fit a VAD, together with major procedures to the heart, thoracic aorta and abdominal cavity. Presently, the risk of such an operation cannot be justified except in the case of those in the most advanced stages of heart failure. With regard to cost, current devices are typically of complex construction and require specialised and expensive manufacturing processes for their construction. The surgery required to lit them is also expensive owing to long and intensive operative procedures.
If the long term implantation of a VAD or an equivalent circulatory assist device could be achieved with a less invasive surgical procedure (e.g. by eliminating any procedures to the abdominal cavity, the need for a sternotomy and/or a heart-lung bypass) and the cost of the devices could be significantly reduced, then the use of VADs to treat heart failure could become far more widespread and routine.
The key to a less invasive implantation procedure for a VAD is to make the device small enough so that it can be comfortably implanted entirely within the pericardial space, eliminating the need for any procedures to the abdominal cavity. Furthermore, a device small enough to be implanted via a thoracotomy, as opposed to a full sternotomy, would be beneficial for those cases where this approach is suitable.
It is also important to minimise surgical risks so it is beneficial to use existing proven to improving on them where possible. A well-proven method of implanting current VADs is attaching the devices directly to the apex of the left ventricle, with an inlet to the device residing within the ventricle and the outlet of the device sitting outside of the heart. This eliminates the need for a separate inflow cannula, reducing the potential for complications. The workings of the pump (impeller, motor, etc.) may reside mostly within the ventricle, across the ventricle wall, or mostly outside of the ventricle depending on the design of the device.
In general terms, a cardiac pump suitable for implantation into a ventricle of a human heart, is known. It is also known for the cardiac pump to comprise a housing comprising an inlet for blood, an outlet for blood and a primary blood flow path, which extends between the inlet and the outlet, and a cardiac pump rotor disposed within the housing for causing blood to flow along the primary flow path from the inlet to the outlet.
In such known devices, the cardiac pump rotor may be rotatably coupled to the housing about plain bearing assemblies. One of the most important factors in the design of a VAD is the passage of blood through the cardiac pump, particularly the passage of blood in the region of the bearings. The regions of blood flow around the bearings, i.e. the regions around circumferential transition between the rotating and stationary components, may be areas of flow stasis and therefore predisposed to thrombus formation or indeed any type of protein deposition. It is particularly important, therefore, that bearings are well washed with a constant supply of fresh blood as the heat generated and geometrical constraints in these areas make them particularly prone to thrombus formation and/or pump deposition.
Therefore, it is desirable to directly expose the interface between rotating and stationary components to a continuous supply of blood flow, such that the proteinaceous and cellular components of the blood responsible for pump deposition and thrombus formation are prevented from aggregating in this region.
U.S. Pat. No. 8,088,059 B2 discloses an axial cardiac pump. A pump similar to that disclosed in U.S. Pat. No. 8,088,059 B2 and known as Jarvik 2000 has supported a patient for seven years and uses blood immersed bearings washed by high flow to avoid excessive thrombus formation. This permits the pump to be very simple and small. Nonetheless, the present Jarvik 2000 bearings and all other mechanical blood immersed bearings of the prior art have a supporting structure that may be susceptible to thrombus adjacent to the bearings.
U.S. Pat. No. 5,399,074 A discloses centrifugal blood pump, used for heart-lung machines or the like, which comprises an impeller, a casing having a suction inlet and a delivery outlet and being equipped with a space for rotatably accommodating the impeller, and a magnetic drive means disposed outside the casing. The impeller is of a rotationally symmetric shape and has a rotary vane section and a cylindrical section equipped with a magnet means. The magnet drive means for generating a rotating magnetic field coaxially encloses the magnet means of the above-mentioned cylindrical section and rotates the impeller in cooperation with the magnet means. At least the end section of the impeller's rotation centre on the rotary vane section side is supported preferably by a pivot bearing. However, the pump disclosed in U.S. Pat. No. 5,399,074 A may also be susceptible to thrombus formation in the regions surrounding the bearings.
The present invention therefore seeks to address these issues.